Orthodontic appliance



May 20, 1969 E. c. FLETCHER 3,444,521

ORTHODONTIC APPLIANCE Filed May 19, 1967 I N VENTOR. fia/m/ 6. Qzms m United States Patent 3,444,621 ORTHODONTIC APPLIANCE Erwin C. Fletcher, La Jolla, Calif., assignor to Unitek Corporation, Monrovia, Calif., a corporation of California Continuation-impart of application Ser. No. 405,065, Oct. 20, 1964. This application May 19, 1967, Ser. No.

Int. Cl. A61c 7/00 US. Cl. 32-14 2 Claims ABSTRACT OF THE DISCLOSURE An orthodontic arch wire composed of three strands of wire twisted together only sufiiciently to form the strands into three interlocking helices which stay interlocked when the twisting moment is relaxed, the strands having diameters in the range of from about 0.007 inch to about 0.010 inch to form a cable-like arch wire having a diameter in the range of about 0.015 inch to about 0.022 inch which substantially fills the slot of an orthodontic tooth bracket.

RELATED APPLICATIONS This is a continuation-in-part of my application Ser. No. 405,065 filed Oct. 20, 1964 and now abandoned, which application was a continuation of my copending application Ser. No. 237,149 filed Nov. 13, 1962, now abandoned.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to orthodontic arch wires of the type to be engaged with a bracket attached to a tooth band to apply a displacing force to the tooth on which the band is mounted.

Description of the prior art In typical orthodontic work, a separate tooth band is mounted around each tooth under treatment. A bracket is attached to the tooth band, and has a channel or slot in it to receive an arch wire which extends through the slots in the brackets. The wire is secured to each bracket so that stresses applied to the Wire are transmitted to the body and to the band to move the teeth to the desired positions. In one orthodontic technique, stress is applied to the arch wire by placing it under tension and stressing it within its elastic limit. The wire is thereafter secured in the stressed condition to brackets, and applies force to the brackets until the wire returns to its original unstressed condition. The smaller the wire, the more it can be stressed without exceeding its elastic limit, but the less its strength and the poorer fit it makes in the typical bracket slot, which is usually of standard size to facilitate mass production, such size being such as to accommodate larger wires often used in the later stages of treatment. For example, in the early stages of treatment of malocclusion of the teeth, usually the teeth are displaced considerably from the preferred final arch form in the patients mouth. It often happens, unless an extremely small diameter arch wire is used to start the treatment, that when the arch wire is tied to the bracket of each tooth, the deflection of this arch wire is so severe that the elastic limit of the wire is exceeded and the wire becomes bent at the time of installation, thereby destroying part of its effectiveness, This requires the orthodontist to change arch wires frequently as each successive wire moves the teeth to the limit of its ability. Not until the teeth are fairly well in line can a wire large Ice enough to fill the bracket channel be used, and the real control of tooth movement be begun.

Especially in the edgewise technique of orthodontia where the wire channel is of a fixed width and depth and is quite large, generally 0.022 or 0.018 inch wide, the very small diameter wires presently used initially to move the teeth generally into line with the desired arch curve fit so loosely in this large channel as to give very little directional control of tooth movement. But, the small diameter wire must be used to obtain the flexibility required. In an attempt to improve the degree of control, several small parallel wires are sometimes used to fill the bracket channel. The manipulation and installation of these parallel wires is very difiicult and time-consuming, since they are in effect individual wires and cannot be handled as an integral unit. For example, it is not feasible to be bend loops in the multiple parallel wires, and the ends of the parallel wires must be soldered together to avoid spreading and forming frayed ends which can prick and cut the interior of a patients cheek.

SUMMARY OF THE INVENTION The ideal situation in initial treatment is a wire of great flexibility, yet of large diameter. Among the materials suitable for orthodontic arch wires, no metal will supply both these characteristics in a single strand. Stiffness increases by the square of the diameter, and stiff wires in early treatment cause pain by forcing too rapid movement of the teeth. On the other hand, a large wire which fills the bracket channel gives control of tooth movement in several directions simultaneously. For instance, at the same time the teeth are being moved to the preferred arch shape, they can also be uprighted and rotated to the preferred final position to speed treatment.

This invention provides an orthodontic appliance in which the arch wire has the major desired advantages of the large wire and small wire, without the disadvantages of either, and without the disadvantages of parallel strands.

The appliance of this invention uses a bracket, which may be of conventional construction, in combination with an arch wire that is made up of three twisted filaments or strands of wire of relatively small diameter twisted together only sufficiently to form interlocking helices disposed about a common, substantially straight, longitudinal axis, which helices do not disengage from each other when the force used in the twisting step is removed from the strands. The wire strands are twisted beyond their elastic limits only such an amount as is required to impart to the strands a set adequate to keep the individual wire from unstranding. The strands are not twisted so tightly that the arch wire itself forms a helix when the strand twisting moment is removed from the strands.

The twisted strands form a contiuous arch wire or cable of any desired diameter, and yet with much greater flexibility and elasticity than would be exhibited by a single-strand wire of the same effective diameter. The diameter of the twisted-strand wire used in this invention can be selected to fill the bracket slot or channel and still retain the flexibility and elasticity of a smaller, singlestrand wire. Moreover, the longer etfective working length of twisted wire between adjacent brackets due to the spiraling of the twisted strands increases flexibility and enhances the elastic stress available in stressing the wire to apply moving forces to the teeth.

Another advantage of the wire made from twisted strands is that it is easier to handle and secure to the bracket than arch wire made of multiple parallel strands. The twisted-strand wire can also be bent to form loops, which is not possible with the multiple parallel-strand wire. Hooks may be soldered to the stranded wire, which is not conveniently done with parallel multiple-strand wire. The ends of the stranded wire remain stranded without the need for solder and the like and do not readily fray to irritate and cut the interior of the patients cheek. Another advantage of the stranded wire is that it can be handled as a single wire. On the other hand, wires of multiple parallel strands have to be made for the individual case with all ends soldered or welded together 1n order to handle them. Another advantage of the stranded wire is that it can be rolled flat or rectangular to fit the slot, which usually has flat sides and bottom, and thereby gives even better control of applied torque and root tipping. The twisted-strand wire may also be preformed at the factory to average arch shape, and its flexibility is easily controlled by varying the diameter of the strands twisted to make the wire. Finally, a single arch using wire of twisted strands in accordance with this invention carries an orthodontic case further toward completion than several changes of single arch wires made of a single strand.

I have found that the optimum arch wire uses three component strands.

Briefly, the invention provides an orthodontic arch wire for use in combination with an orthodontic bracket having a channel formed therein. The arch wire consists of a cable defined by three wire strands twisted together to form three interlocking helics disposed about a common, substantially straight, longitudinal axis of the cable. The strands are twisted together only sufficiently to assure that the helices do not unstrand from each other in use of the arch wire. The strands are formed of wire having diameters in the range of from about 0.007 inch to about 0.010 inch, and the arch wire has a diameter in the range of from about 0.015 inch to about 0.022 inch to fit snugly in the channel of an orthodontic bracket to transmit stress developed in the arch wire in use to a tooth to which the bracket is mounted.

DESCRIPTION OF THE DRAWING The above-mentioned and other aspects of the invention will be more fully understood from the following detailed description and the accompanying drawing which shows the present arch wire ligated into the slot of an orthodontic bracket mounted on a tooth band.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, an orthodontic bracket 12, which may be of conventional type such as that disclosed and claimed in U.S. Patent No. 2,713,720, includes a body 14 having a pair of oppositely extending flanges 16 which form a base surface shaped to fit and be welded to a conventional tooth band 18. The tooth band makes a snug fit around a tooth (not shown) to which it is to be applied. The bracket may be of other types, such as those which do not include flanges on the bottom, but the illustrated embodiment is a preferred construction because it enables the bracket to be spot welded to the tooth band. This is considered by many to be superior to the soldered connection required if the body is not provided with flanges.

The outer surface 20 of the body is referred to as the labial surface," and this terminology is used throughout the following description and claims. The labial portion of the body includes a pair of laterally extended and overhanging lips 22, which extend transversely to the flanges that form the base. The undersurfaces of the lips are concave downwardly to receive a conventional tie wire 24 which holds a longitudinally extending arch wire 26 in place in a longitudinal channel or slot 28 in the labial surface of the bracket.

The bracket channel is rectangular in cross section. The arch wire can either have a natural cross section, i.e., be substantially round, or it can be pressed into a substantially rectangular cross section. In either case, the

wire preferably fills the channel, i.e., the wire engages the sides and bottom of the channel throughout substantially the entire channel length, to improve the transmission of force from the wire to the bracket.

The wire is made of three twisted strands or filaments 29, and may be pressed or rolled to a flat or rectangular shape to make a close fit against the sides and bottom of the bracket channel. The three strands 29 are twisted together only sufiiciently beyond their elastic limits as is necessary to impart to the strands only sufiicient permanent set adequate to form the strands into three simple interlocking helices disposed about a common, substantially straight axis. For the purpose of defining this invention, the term substantially straight axis is used to mean an axis which deviates from linearity only as is necessary for the arch wire to extend through the bracket channels. The strands of the wire remain interengaged with each other when the twisting moment is removed from the set strands.

The size of the filaments in the wire can be varied to meet diiferent requirements. For example, the elasticity of an arch wire is changed by varying the diameter of the strands, e.g., a wire having an effective outside diameter of 0020-0021 inch is easily made up of three twisted strands which are each 0.010 inch in diameter. A wire of 0.0175 inch outside diameter is made of three twisted strands of 0.008 inch outside diameter, and a wire of 0.0195 inch outside diameter is made of three twisted strands of 0.009 inch outside diameter.

The arch wire in this invention has an eifective outside diameter or maximum transverse dimension in the range of about 0.015 to about 0.022 inch, and is made up of three strands having individual outside diameters ranging between about 0.007 and about 0.010 inch.

Optimum practice of this invention is obtained using three wire strands 29. It has been found that an even number of wires do not strand together evenly when the several strands are twisted to form the arch wire, that is, an arch wire made of an even number of strands has an uneven external configuration. Where two strands are used, the arch wire resembles a twisted ribbon or tape. Where four strands are used, the configuration of the arch wire resembles a twisted square bar. In either case, the uneven configuration of the arch wire means that the wire does not always fit snugly in the slot of an orthodontic bracket; also, unevenly configured arch wires do not slide readily in bracket slots as is often desired during the initial stages of orthodontic treatment. Arch wires made of five or more strands have too much flexibility because the individual strands are of very small diameter if the arch wire is to have the desired ovenall diameter.

The wire and bracket arrangement shown and described has several advantages over the prior appliances in which single strand wire or multiple parallel strand wire is used. The twisted strand wire in accordance with this invention provides the desired increase in strength and effective cross sectional area, and yet retains flexibility and elasticity of much smaller diameter wire. This means that the twisted wire can be subjected to greater elastic extension than the single filament wire, and therefore will apply larger corrective displacement between arch changes than is possible for the single strand wire. Moreover, the twisted strand wire in accordance with this invention retains the advantages of the single strand wire because it is easier to handle and to tie into brackets than multiple parallel strand wire and can be bent into the loops, which is not possible in multiple parallel strand wire. In addition, hooks may be soldered to the twisted strand Wire. As noted, the twisted strands remain stranded and do not fray to form irritating ends which could prick and cut the cheek of the patient.

Finally, the twisted strand wire may be rolled to form flat sides or rectangular cross section to make a close fit in the bracket slots and give improved torque and root tipping.

I claim:

1. In combination with an orthodontic bracket adapted for attachment to a tooth and having a channel therein, the improvement in an orthodontic arch wire of elongated twisted strands disposed in the channel for transmission of stress developed in the arch wire to the orthodontic bracket, the arch wire consisting of a cable of only three elongated strands twisted to form. three interlocking helices disposed about a common substantially straight longitudinal axis of the cable, the strands being twisted only sufficiently to maintain said helices in the respective strands upon removal of a twisting force from the strands, the strands having outside diameters in the range of from about 0.007 inch to about 0.010 inch and the cable having an effective diameter in the range of from about 0.015 inch to about 02-022 inch to cooperate closely with the channel in the orthodontic bracket.

2. An orthodontic arch wire for use in the channels of orthodontic tooth brackets and consisting of a cable of only three elongate wire strands twisted together to form three interlocking helices disposed about a common straight longitudinal axis of the cable, the strands being twisted beyond their elastic limits only so far as to impart to the strands a permanent helical set adequate to maintain the helices interlocked with each other upon removal of a twisting force from the strands, the strands having diameters in the range of from about 0.007 inch to about 0.010 inch and the cable having an effective diameter in the range of from about 0.015 inch to about 0.022 inch to cooperate snugly with the channels of orthodontic tooth brackets.

9/1962 Wallshein. 3/1964 Rubin.

ROBERT PESHOCK, Primary Examiner. 

